The present invention relates to a method for making semiconductor devices, particularly those that include copper interconnect pads that have aluminum caps.
One way to connect a semiconductor die to the device""s package is to wirebond an interconnect pad, which is located on the die, to the package. When copper is used to make such an interconnect pad, the copper may oxidize if exposed. Consequently, to make a copper containing interconnect pad, an aluminum cap may be formed on the copper to protect it from oxidation. The wirebond is then made to the aluminum cap.
The conventional process for forming an aluminum cap on a copper containing interconnect pad includes the following steps. Copper is deposited onto a dielectric layer to fill a trench that has been formed in that layer. The copper is then polished to remove it from the surface of the dielectric layer to generate a structure in which the surface of the remaining copper is substantially flush with the surface of the dielectric layer. Aluminum is deposited onto the surface of the copper and the adjoining dielectric layer. Next, a lithography and etch process is used to remove the aluminum from the dielectric layerxe2x80x94retaining it on top of the copper only. After conventional post etch photoresist ash and clean steps, a passivation layer is formed on top of the resulting structure.
The conventional process for forming aluminum caps on copper containing interconnect pads is relatively expensive and complex. In addition, because the structure, which this process creates, includes aluminum caps that rise above the surface of the dielectric layer, relatively narrow gaps may separate adjacent caps. It may be difficult to fill those gaps with the passivation layer that is deposited over the aluminum caps and the dielectric layer. To fill them, the passivation layer may have to be deposited using a high density plasma process. That layer may then have to be planarized. This adds still more complexity to the process.
Accordingly, there is a need for a relatively inexpensive and less complex process for making a semiconductor device that includes aluminum capped copper interconnect pads. There is also a need for such a process that generates an aluminum capped structure in which the surface of the cap is substantially flush with the surface of the adjacent dielectric layer. The present invention provides such a process.